PCR Primer Design & Optimization

Question 1

What is the optimal melting temperature (Tm) range for most PCR primers?

Accepted Answer

55–65°C

Answer

45–50°C

Answer

70–80°C

Answer

80–90°C

Question 2

Which of the following primer characteristics is most likely to cause primer-dimer formation?

Accepted Answer

Complementarity between the 3' ends of forward and reverse primers

Answer

High GC content at the 5' end

Answer

A Tm difference of 2°C between primers

Answer

Primer length of 20 nucleotides

Question 3

What GC content range is generally recommended for PCR primers?

Accepted Answer

40–60%

Answer

20–30%

Answer

65–75%

Answer

80–90%

Question 4

Why is it generally advisable to end a primer with a G or C nucleotide at the 3' terminus?

Accepted Answer

A G or C clamp stabilizes primer-template binding at the extension site

Answer

G and C improve primer solubility in aqueous solution

Answer

Pyrimidines at the 3' end reduce polymerase error rates

Answer

G and C nucleotides are more efficiently phosphorylated

Question 5

The annealing temperature (Ta) in a PCR protocol is typically set how many degrees below the primer Tm?

Accepted Answer

5–10°C

Answer

1–2°C

Answer

15–20°C

Answer

25–30°C

Question 6

Which formula is most commonly used to estimate primer Tm for short oligonucleotides (< 14 bp)?

Accepted Answer

Wallace rule: Tm = 2(A+T) + 4(G+C)

Answer

Nearest-neighbor thermodynamic model

Answer

Henderson-Hasselbalch equation

Answer

Arrhenius equation

Question 7

What is the primary purpose of performing a gradient PCR when optimizing primer annealing?

Accepted Answer

To identify the annealing temperature that yields the highest specificity and yield

Answer

To determine the optimal extension time for the product

Answer

To measure primer concentration effects on amplification

Answer

To test the stability of the DNA template